Conventional railroads in the United States and elsewhere are typically formed by a compacted sub-grade, a bed of gravel ballast, wooden cross-ties positioned upon and within the ballast, and parallel steel rails secured to the ties. Variations of construction occur at road and bridge crossings and in other circumstances. The ballast beneath and between the ties stabilizes the positions of the ties, keeps the rails level, and provides some cushioning of the composite structure for loads imposed by rail traffic. Vibrations from the movement of tracked vehicles over the rails and weathering from wind, rain, ice, and freeze and thaw cycles can all contribute to dislodging of some of the ballast over time. Thus, in addition to other maintenance activities, it is necessary to replace ballast periodically to maintain the integrity and safety of railroads.
Ballast has been spread in the past using specially designed ballast hopper cars which include a hopper structure holding a quantity of ballast, a ballast chute communicating with the hopper, and a power operated ballast discharge door in the chute. The door can be controlled to selectively open or close to control the discharge of ballast. In some designs, the discharge door can be controlled to open outboard toward the outside of the rails, to close, or to open inboard toward the inside between the rails. Typical ballast hopper cars have a front hopper and a rear hopper, and each hopper has two transversely spaced doors, one to the left and one to the right. Thus, each hopper door can be controlled to discharge ballast outside the rails on the left and/or the right or between the rails. A typical configuration of a ballast hopper car is described in more detail in U.S. Pat. No. 5,657,700, which is incorporated herein by reference.
Ballast spreading has most often been controlled manually in cooperation with human spotters who walk alongside the moving ballast cars to open or close the ballast doors as necessary. A more recent ballast spreading control technique is by the use of a radio linked controller carried by an operator who walks alongside the moving ballast cars. Both conventional control methods are slow and thus disruptive to normal traffic on the railroad section being maintained, thereby causing delays in deliveries and loss of income.
U.S. Pat. No. 6,526,339 to Herzog, et al. generally discloses methods for spreading railroad ballast with location control based on data received from the global positioning system or GPS. The GPS system, is a “constellation” of satellites traveling in orbits which distribute them around the earth, transmitting location and time signals. As originally designed, a GPS receiver, receiving signals from at least four satellites, was able to process the signals and triangulate position coordinates accurate to about ten to twenty meters. Current generations of commercially available GPS receivers, using differential GPS techniques, are able to achieve accuracies in the range of one to five meters. Such accuracy is adequate for depositing ballast where desired and inhibiting the deposit of ballast where it is not desired. Additional information regarding the development of GPS technologies can be obtained from U.S. Pat. No. 4,445,118 and U.S. Pat. No. 5,323,322. Development of the GPS system referred to herein was sponsored by the United States government. However, satellite based positioning systems developed or operated by other nations are also known.
Because railroad companies typically maintain hundreds or thousands of miles of track on a recurring schedule, the ballast replacement component of track maintenance alone can be a major undertaking in terms of equipment, materials, traffic control, labor, and management. Implementation of a GPS based system of the type disclosed in U.S. Pat. No. 6,526,339 can increase the accuracy and efficiency of ballast application on railways, however, the use of other techniques for controlling the application of ballast can be as good as GPS techniques and, in some applications, even better in some respects.